1. Field of the Invention
This disclosure relates to a wireless access system, and particularly to a method and apparatus for updating E-MBS system information.
2. Related Art
FIG. 1 illustrates an example of a frame structure.
Referring to FIG. 1, a superframe (SF) includes a superframe header (SFH) and four frames F0, F1, F2, and F3. The frames of the superframe may have the same length. Although the size of each superframe is 20 ms and the size of each frame is 5 ms, the present invention is not limited thereto. The length of the superframe, the number of frames included in the superframe, and the number of subframes included in a frame may be variously changed. The number of subframes included in a frame may be variously changed depending on the channel bandwidth and a cyclic prefix (CP).
One frame includes a plurality of subframes SF0, SF1, SF2, SF3, SF4, SF5, SF6, and SF7. Each subframe may be used for uplink or downlink transmission. One subframe includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols or orthogonal frequency division multiple access (OFDMA) in the time domain and a plurality of subcarriers in the frequency domain.
The OFDM symbol is to represent one symbol period and may be referred to by other terms, such as OFDMA symbol or SC-FDMA symbol, according to the type of multiple access scheme.
The subframe may consist of 5, 6, 7, or 9 OFDMA symbols, but this is merely an example, and the number of OFDMA symbols included in the subframe is not limited. The number of OFDMA symbols included in the subframe may be variously changed depending on the channel bandwidth or the length of CP.
Depending on the number of OFDMA symbols included in the subframe, the type of subframe may be defined. For example, type-1 subframe may be defined to include 6 OFDMA symbols, type-2 subframe to include 7 OFDMA symbols, type-3 subframe to include 5 OFDMA symbols, and type-4 subframe to include 9 OFDMA symbols. One frame may include subframes having the same type. Or, one frame may include subframes having different types. That is, the number of OFDMA symbols included in each subframe of one frame may be the same or different. Or, the number of OFDMA symbols of at least one subframe in one frame may be different from the number of OFDMA symbols of the remaining subframes in the frame.
A time division duplex (TDD) scheme or a frequency division duplex (FDD) scheme may apply to the frame. In the TDD scheme, each subframe is used for uplink transmission or downlink transmission at different times at the same frequency.
That is, in the TDD scheme, the subframes in the frame are separated into uplink subframes and downlink subframes in the time domain. In the FDD scheme, each subframe is used for uplink transmission or downlink transmission at different frequencies at the same time. That is, in the FDD scheme, the subframes in the frame are separated into uplink subframes and downlink subframes in the frequency domain. The uplink transmission and the downlink transmission take up different frequency bandwidths and may be performed at the same time.
SFH may transport essential system parameters and system configuration information. SFH may be positioned in the first subframe of the superframe. SFH may occupy the last five OFDMA symbols in the first subframe.
The superframe header may be classified into primary SFH (P-SFH) and secondary SFH (S-SFH). P-SFH and S-SFH may be transmitted per superframe. S-SFH may be transmitted in two consecutive superframes. Information transmitted through S-SFH may be divided into three sub-packets S-SFH SP1, S-SFH SP2, and S-SFH SP3. Each sub-packet may be periodically transmitted at different periods. Pieces of information transmitted through S-SFH SP1, S-SFH SP2, and S-SFH SP3, respectively, may have different degrees of importance, and S-SFH SP1 may be transmitted at the shortest period, and S-SFH SP3 may be transmitted at the longest period.
S-SFH SP1 includes information on network re-entry.
S-SFH SP2 includes information on initial network entry and information on network discovery. S-SFH SP3 includes the remaining critical system information.
One OFDMA symbol includes a plurality of subcarriers, and the number of subcarriers is determined depending on the FFT size. There are several types of subcarriers. The types of subcarriers may be classified into data subcarriers for data transmission, pilot subcarriers for various ways of estimation, and null carriers for guard bands and DC carriers.
16m E-MBS(Enhanced Multicast and Broadcast Service)
The enhanced multicast and broadcast service (E-MBS) provides a user group of using common multicast station identifier (MSTID) and a flow identifier (FID) with an efficient method for simultaneous transmission of common downlink data. E-MBS is provided only for downlink, and may be coordinated or synchronized between base stations that belong to one group to permit macro diversity.
Each E-MBS connection is associated with the service flow provided together with the traffic parameters and quality of service (QoS) for the service flow. Service flows transmitting E-MBS data may be described as an example for individual terminals participating in the service while the terminals perform common operation. Through such description, the terminal identifies the service and learns the parameters associated with the service flow.
Each base station that may provide an E-MBS service belongs to a specific E-MBS zone, and one base station may belong to a plurality of E-MBS zones. The E-MBS zone is defined as one set of base stations which use the same MSTID and FID to transmit content of a specific service flow. Each E-MBS zone is distinguished from others by a unique E-MBS zone ID.
To assure the proper multicast operation over a network in which a base station supporting the E-MBS service is positioned, the MSTIDs and FIDs used for common E-MBS content and service should be the same for all the base stations in the same E-MBS zone.
This permits a terminal registered for a specific service to receive seamless E-MBS transmission in the E-MBS zone even without performing re-registration with another base station in the E-MBS zone or without performing uplink communication.